Selective copper solvent for diolefin extraction



Patented Dec. 21, 1948 SELECTIVE COPPER SOLVENT FOR DIOLEFIN EXTRACTIONCharles E. Morrell, Westfleld, and Miller W. Swaney, Cranford, N. 1.,assignors to Standard Oil Development Company, a corporation of DelawareNo Drawing. Application December 29, 1945, Serial No. 638,518

Claims. 1

This invention relates to improvements in the separation of olefins frommixtures of hydrocarbons and relates particularly to improvements in theseparation of olefins or diolefins from hydrocarbons having two or morecarbon atoms to the molecule by the use of copper solvents.

The ailinity of certain cuprous compounds for unsaturated hydrocarbonsis well known. Thermally decomposable complexes are formed between thesimple olefins and diolefins and cuprous compounds such as cuprouschloride, CuCl.NH4C1 complexes, etc. However, most of these cuprouscompounds and complexes possess certain features such as corrosivenessto metal equipment which render them unsuited for use in the commercialrecovery and separation of olefins and diolefins in hydrocarbonfractions.

The use of hydroxy amine complexes of copper for the separation ofolefins from mixtures of hydrocarbons is suggested in the U. S. Patent2,005,500, issued June 18, 1935, to Walter Philip Joshua and HerbertMuggleton Stanley. However, the hydroxy amine copper solutions areunstable on heating to temperatures of the order of 80 C., which arerequired for satisfactory desorption of the hydrocarbons from thesolutions.

In U. S. application Serial No. 371,998, filed December 27, 1940, for C.E. Morrell and M. W. Swaney, is disclosed the efllcacy of the ammoniacalcuprous acetate solutions of high cuprous content for the extraction andseparation of butadiene from cracked hydrocarbons fractions. Thesesolutions possess high solvency for butadiene, high specificity forbutadiene over the butylenes, and high thermal stability in glass or insteel equipment. However, these ammoniacal cuprous acetate solutionspossess considerably lower solvency for the higher diolefins such asisoprene, piperylene, etc.

According to this invention it is now discovered that if the ammonia inthe ammoniacal cuprous acetate complexes is replaced by monomethylamine, in part or wholly, the resulting complex is very effective forthe extraction and concentration of the higher dioleflnssuch as isoprenefrom hydrocarbon mixtures. In addition, the basic monomethylaminecuprous acetate solutions retain remarkable thermal stability and arenon-corrosive to metal equipment, for example, steel.

The superior features of the monomethylamine cuprous acetate solutionsfor the absorption and separation of diolefins from hydrocarbons areillustrated by the following examples. but this An. ammoniacal cuprousacetate solution of high ammonia, acetate and copper contents wasprepared containing 3.4 mols of cuprous copper per liter. This solutionpossessed the capacity to absorb about 25 gaseous volumes of purebutadiene at 0 C. per volume of solution. When brought to equilibrium at0 C. however, with a liquid mixture containing 25% isoprene/%trimethylethylene (2-methylbutene-2) and subsequently desorbed byheating followed by removal of ammonia and blending of the C5 withnitrogen to facilitate analysis, it was found to have dissolved only 1.6volumes of (gaseous) C5 per volume of copper solution, the purity of theisoprene desorbate being 78%, or the equivalent of 0.36 liters ofisoprene vapor/mol of cuprous complex.

Example 2 A methylamine-cuprous acetate complex solution containingapproximately 16 molar methylamine, 3 molar acetate, and 1.24 molartotal copper (1.0 molar cuprous) contents was brought to equilibriumwith a blend of 24% isoprene-76% pentene-1 at 0 C. In order todemonstrate the superiority of this methylamine solution, pentene- 1 wasemployed as the C5 diluent rather than trimethylethylene of Example 1,since the former (pentene-1) is approximately ten times as soluble inthese copper solutions as the latter (trimethylethylene) and thereforepentene 1 isfar more difficult to separate from isoprene. Under theabove extraction conditions the methylaminecuprous acetate solutionabsorbed 4.5 volumes of gaseous C5 of 63% isoprene content per volume ofcopper solution employed. In terms of pure isoprene vapor this isequivalent to an absorption of 2.8 liters of C5 gas/mol of cuprouscomplex. Therefore, the methylamine solution was approximately 8 timesas eflicient as the ammoniacal complex for absorbing isoprene. Themonomethylamine cuprous acetate solution employed in this examplepossessed a very high thermal stability under confinement and wasnon-corrosive to steel.

The process herein cited may also be applied to other mixtures ofdiolefins and to other cuprous salt solutions. It is particularlyadapted for separating unsaturated hydrocarbons, such as ethylene,propylene, butene-l, butene-2, isobutylene, allene, butadiene, isoprene,piperylene, etc.,

dimethylbutadiene, and the methyl pentadienes from a relatively moresaturated hydrocarbon.

' used varies irom'l.5 to 7; 2.0 to 3.5 being preferred. The watercontent that may be used varies from to 20 mols per liter; 1.5 to 7 molsper liter being preferred. The cuprous content is between about 1.0 to2.5 mols per liter, preferably between 1.5 to 2.0 mols per liter. Thepresence Of some cupric copper is desirable to the The alkylamines that"2. The process for separating a C6 dioleiin from a C5 mono-olefin in amixture thereof which comprises absorbing principally the diolefln in anaqueous solution of a primary alkyl amine cuprous salt complex in whichthe alkyl amine has from 1 to 4 carbon atoms per molecule, said solutionhaving a pH value above about 10, separating the resulting solution ofthe absorbed diolefin from the remainingmixture of concentrated C5monoolefin, and desorbing the C5 diolefln from the thus separatedsolution.

3. A process as described in claim 2, in which the diolefln is isopreneand the alkyl amine is mono-methylamine.

4. The process as described in claim 2, in

, which the C5 diolefin is piperylene.

solution stability and a pH above about 10 is desirable.

The extraction with these solutions may be carried out most convenientlyat temperatures just above the freezing points of the solutionssaturated with olefin which are usually below 0 C. When the higherextraction temperatures are employed the operations may be carried outunder applied pressure to prevent loss of amine.

Regeneration is carried out conveniently around 50-80" C. using adiluent gas, though no diluent gas other than the amine is needed, andhigher or lower desorption temperatures may be used under appropriatepressures.

Hence, monomethylamine cuprous acetate solutions offer most promise forconcentrating isoprene produced by catalytic dehydrogenation oftrimethylethylene but are also applicable for treatment of C5 fractionsobtained by thermal and catalytic cracking of heavier hydrocarbons.

What is claimed is:

l. A process for separating a C5 diolefin from a C5 mono-olefin in amixture thereof which comprises selectively absorbing the C5 diolefin inan alkyl amine cuprous salt complex solution having a pH valueabove-about 10, leaving the C5 monoolefin undissolved by said solutionfreed of the absorbed C5 diolefin.

5. The process of separating isoprene from pentene-l in a hydrocarbonmixture thereof which comprises selectively extracting said isoprene ina mono-methylamine-cuprous acetate complex solution at a temperaturerange from the freezing point of the solution up to about 0 C., saidsolution having a 1.0 to 2.5 molar cuprous content with a mo] ratio of2.0 to 3.5 of

the amone to 1 mol of acetate, separating said solution containing theextracted isoprene from 'the hydrocarbon mixture, anddesorbing theisoprene irom the'solution.

CHARLES E. MORRELL. MELER W. SWANEY.

REFERENCES CITED The following references are, of record in the file ofthis patent;

UNITED STATES PATENTS Asbury et 8.1 June 11, 1946

